The present invention relates to a liquid cooling system for cooling a body that is generating heat, and, in particular, to a liquid cooling system that is suitable for use in a small and/or thin electronic device.
Semiconductor devices that are used in electronic devices, such as a computer, etc., generate heat during their operation. In particular, high-integrated semiconductor devices, in recent years, have produced an increased amount of heat generation. Since the semiconductor device will be damaged if the temperature thereof exceeds a certain value, cooling is necessary to prevent damage to the semiconductor device having a large amount of heat generation during use.
For cooling the semiconductor device of an electronic apparatus, there are various known techniques, such as thermal conduction or air-cooling, or the use of a heat pipe, or liquid cooling.
Cooling by thermal conduction can be achieved by using materials having a large thermal conductivity along the heat radiation route, extending from the semiconductor device to the outside of the electronic apparatus. This method has been suitable for a so-called compact electronic apparatus, in which heat generation is relatively small, such as a notebook-type personal computer.
With cooling by the use of forced air, an air blower or fan is provided inside the electronic apparatus, thereby achieving a cooling of the semiconductor device therein by forced circulation of air thereon. This method is adopted widely for the cooling of semiconductor devices having a higher amount of heat generation, and it also has been applied to a personal computer by making the air blower small and thin in size.
Cooling with the use of a heat pipe, involves carrying heat out the outside of the electronic apparatus by means of coolant enclosed within a pipe, as described in Japanese Patent Laying-Open No. Hei 1-184699 (1989), and Japanese Patent Laying-Open No. Hei 2-244748 (1989), for example. With this method, since there is no part capable of consuming electric power therein, such as an air blower or fan, such a cooling device has good efficiency, i.e., it increases the cooling through thermal conduction. However, with this method, there is a limit to the amount of heat that can be transferred.
Cooling by means of a liquid coolant is suitable for the cooling of a semiconductor device which generates a large amount of heat, and such a cooling device is described, for example, in Japanese Patent Laying-Open No. Hei 5-1335454 (1993), Japanese Patent Laying-Open No. Hei 6-97338 (1994), Japanese Patent Laying-Open No. Hei 6-125188 (1994), and Japanese Patent Laying-Open No. Hei 10-213370 (1998). However, such a cooling system using a liquid coolant has been restricted as to its field of utilization, such as to a large-scale computer. This is because the cooling system using a liquid coolant requires a large number of parts, such as a pump, a pipe system, heat radiation fins, etc., which are used exclusively for cooling, and so the apparatus comes to be large in size. Thus, it is difficult to maintain a satisfactory reliability when using liquid for cooling compared to other methods. It is also one of the reasons why, on the commercial market, no semiconductor device requiring such a high level of cooling employs a liquid cooling system, other than in the field of large-scale computers.
A technique for adapting liquid cooling to a small-sized apparatus, including a notebook-sized personal computer, is described in Japanese Patent Laying-Open No. Hei 6-266474 (1994). In this cooling device, a header attached onto the semiconductor device and a heat radiation pipe separately located from it are connected with each other by means of a flexible tube to form a cooling system, wherein heat is transferred through the liquid coolant flowing therein, thereby cooling the semiconductor device.
However, there has been a remarkable increase in the heat generation produced from semiconductor devices which are used in electronic devices, such as a personal computer, a server computer, a work station, etc., in recent years, with the result that adoption of such conventional technique for cooling is no longer sufficient in connection with electronic apparatuses that are required to be small and thin in size, in particular, such as a notebook-type personal computer.